The logic is simple: the is the largest airliner in the skies today. It has a potential capacity of 850 passengers. If the plane is full and you can divide the flight’s emissions by 850, you’re getting the most carbon efficient form of air travel available on the market, something Airbus like to highlight. But most carriers don’t go for 850 passengers, because they choose to put larger seats with more space in, and carry fewer passengers at a higher price.

At the more extreme end comes Etihad’s configuration, which has 417 economy class seats downstairs, 70 business class seats, then a handful of first class ‘apartments’, and finally a three room suite. If you divide the flight’s carbon emissions by the square footage that passengers occupy, then those in the most expensive seats have footprints than those in economy. Luxury air travel takes up space, and is much more carbon intensive than standard.

If you want to reduce aviation emissions, get more people on planes. This principle is why than ‘legacy carriers’ such as British Airways, who tend to market themselves through luxury and legroom.

First class travel isn’t going to be banned. There’s no mechanism to do that as far as I can see. But there are various approaches that might help to discourage it. First of all, we can choose not to book the bigger seats. For most of us that’s not an option anyway, but there are environmental benefits to squeezing in. If you must fly, try and book with airlines that don’t have business or first class seats.

Another useful step would be for businesses, government and organisations to implement an economy class policy for their staff. The World Bank did some very and the emissions savings they made from shifting away from first class. It might be unpopular with staff if they’re used to the luxury, but if they have to slum it economy class they might think twice about whether or not they actually need to go at all. Changing the policy would reduce emissions per flight, but may well reduce flying overall.

Aviation isn’t taxed, so there’s no way to implement a tax on first class seats. Airport taxes are one way around that, and Britain has different tax bands for different classes of travel. Similar taxes can be implemented where they aren’t already, and the difference between bands can be extended.

Since we can’t make flying sustainable right now, we need to make the best possible use of the planes that we have, cutting emissions where we can. Limiting the number of luxury seats is one of the easiest things we can do.